JPH0919620A - Harmful gas removal method - Google Patents

Abstract

(57) [Abstract] [Purpose] A harmful gas such as a volatile inorganic hydride, a halide, or an organometallic compound can be detoxified only by plasma treatment, and a plasma treatment device can be produced without generating a new harmful substance. Provided is a method for removing harmful gas by plasma treatment capable of capturing harmful components therein. A plasma is generated between a cathode 20 and an anode 30 provided in a low pressure discharge vessel 10, and exhaust gas containing harmful components is introduced into the plasma, and the cathode is cooled to a predetermined temperature. Is heated to a predetermined temperature. The harmful components become positive ions by the plasma, and finally form an alloy or compound with the substance forming the anode, and are trapped as a film on the anode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing harmful gases, and more particularly, it uses a plasma of exhaust gas containing harmful components such as volatile inorganic hydrides, halides and organometallic compounds used as semiconductor material gas. It relates to a method of detoxifying by treatment.

[0002]

2. Description of the Related Art For example, in the manufacture of semiconductor devices, as raw material gases, volatile inorganic hydrides such as silicon, phosphorus, boron, and arsenic, halides, organometallic compounds, etc., may be explosive and toxic to humans. A gas having the same is used.

A semiconductor element is manufactured through many steps. Among them, in the steps such as etching, sputtering, chemical vapor deposition (CVD), etc., the raw material gas is supplied together with a carrier gas under reduced pressure. . All of these raw material gases are not necessarily consumed in the process, and some of them are discharged. In addition, harmful component gas may be produced as a by-product during the process. Therefore, the exhaust gas discharged from each of the above-mentioned steps contains these harmful component gases, and therefore it is necessary to detoxify them before discharging them to the atmosphere.

Regarding the detoxification treatment of the exhaust gas containing the harmful component, the exhaust gas is introduced into a detoxifying agent-filled cylinder filled with a solid detoxifying agent to adsorb the harmful component to the detoxifying agent, or Chemically decomposing or detoxifying methods are used. This method is simple and excellent without requiring a complicated device.

However, when the concentration of harmful components in the exhaust gas is high, it is necessary to dilute it with a large amount of gas (inert gas), and there is no universal detoxifying agent effective for all harmful components.
It is necessary to select an abatement agent according to the harmful components. For example, since there is no harmful agent that effectively adsorbs or decomposes a fluorine-based halide gas, in that case, it is necessary to perform a separate treatment.

Therefore, a method of removing harmful component gas by plasma treatment has been proposed. This plasma treatment is to generate plasma between the cathode and the anode under reduced pressure to generate ions and radicals. Utilizing the plasma treatment can promote decomposition of stable compounds and chemical reactions. . In addition, since the steps such as the etching, sputtering, and chemical vapor deposition in the production of semiconductor elements are performed under reduced pressure, and the exhaust gas is also discharged under reduced pressure, it is introduced into the reduced pressure discharge vessel in the reduced pressure state and plasma treated. It can be said that it is convenient.

[0007] A method of utilizing plasma treatment for removing exhaust gas containing harmful components has been tried for a long time. For example, in the method disclosed in Japanese Patent Laid-Open No. 129868/51, the harmful components are contained. The exhaust gas is plasma-treated in the presence of an oxidant. That is, as a harmful component,
A gas containing a metal hydride such as phosphine, diborane, silane, or arsine is introduced together with oxygen gas into a decompression container, and is converted into plasma to accelerate the oxidation reaction, and in many cases, is converted to solid metal oxide and water. It is disclosed that the solid metal oxide produced is accumulated on the inner wall of the vacuum vessel and removed. For example, silane (SiH ₄ ) is silicon oxide (SiO ₂ ) and arsine (AsH ₃ ) is arsenic oxide (A).
s ₂ O ₃ ), respectively, are converted into solid oxides and removed. However, hydrogen sulfide (H ₂ S) becomes sulfur oxide (SO ₂ ) in the gaseous state, and it cannot be said that it has been rendered harmless.

Further, in the waste gas treatment device described in Japanese Patent Laid-Open No. 58-6231, a waste gas treatment device is provided between a reaction device for discharging exhaust gas containing harmful components and a discharge device for discharging exhaust gas from the reaction device. It is described that a plasma device is arranged and volatile inorganic hydrides such as silane, phosphine, and diborane (B ₂ H ₆ ) are removed by plasma treatment.
Further, JP-A-1-143627 discloses a plasma processing apparatus having an improved structure.

Although the harmful treatment of harmful components using these plasma treatments has been effective for fluorine-based harmful component gases, which are difficult to remove with a solid harm-removing agent, it is difficult to remove them by using fluorine. There was a problem of damage and damage due to the scattering of fluoride. Therefore, in the apparatus described in JP-A-5-103945, the solution is achieved by providing the low-pressure discharge container for plasma treatment with an insulating material and providing electrodes for plasma generation outside the low-pressure discharge container. .

[0010]

In the above-mentioned conventional removal of harmful components by various plasma treatments, plasma treatment promotes chemical reactions such as decomposition of harmful components. For example, difluorosilane, which is difficult to be chemically decomposed, is converted into silicon and fluorine gas by using plasma treatment, nitrogen trifluoride is converted into fluorine gas and nitrogen gas, and silicon tetrafluoride gas is converted into silicon and fluorine gas, respectively. It was removed by decomposing.

That is, the conventional harmful gas removal treatment by the plasma treatment promotes the reaction of chemically converting the harmful components into other compounds by the plasma treatment, and has both advantages and disadvantages. For example, the method described in JP-A-51-129868 is to promote reaction of a metal in a harmful component with oxygen to form an oxide by plasma. For example, when the target harmful gas is silane. Is converted to silicon dioxide and water. Since the produced silicon dioxide is a harmless and stable solid and moisture is also harmless, detoxification can be achieved only by this treatment. But,
A large amount of oxygen gas must be used, and powdery silicon dioxide is generated and pollutes the inside of the vacuum discharge vessel. Moreover,
When hydrogen sulfide is contained as a harmful gas, harmful sulfur oxide is generated by this treatment, so it cannot be said to be harmless.

Further, although there is an advantage that a chemically stable fluorine-based gas can be decomposed into a fluorine gas which can be easily treated by plasma treatment, since the fluorine gas itself is harmful, the fluorine gas is rendered harmless again after the plasma treatment. Will need to be processed.

Therefore, according to the present invention, a harmful gas such as a volatile inorganic hydride, a halide or an organic metal compound can be rendered harmless only by the plasma treatment, and a new harmful substance is not generated in the plasma treatment apparatus. It is an object of the present invention to provide a method for removing harmful gas by plasma treatment capable of capturing harmful components.

[0014]

In order to achieve the above object, the method for removing harmful gas according to the present invention comprises generating plasma between a cathode and an anode provided in a reduced pressure discharge vessel, and generating plasma in the plasma. The exhaust gas containing harmful components is introduced, the cathode is cooled to a predetermined temperature, and the anode is heated to a predetermined temperature.

That is, a cathode provided with a cooling means and an anode provided with a heating means are arranged in a reduced pressure discharge vessel,
While the cathode is cooled to a predetermined temperature and the anode is heated to a predetermined temperature, a predetermined potential is applied to generate plasma, and volatile inorganic hydrides, volatile inorganic halides, organometallic compounds and other harmful substances are generated in the plasma. When the exhaust gas containing a component is introduced, the harmful component is cationized, and the generated cation acts on the cathode or the anode to alloy with the cathode constituent atoms sputtered from the cathode to form a film-like or granular form. Captured on the anode.

As the harmful component to be subjected to the detoxification treatment in the present invention, various ones can be mentioned, in particular, various gases used in the semiconductor element manufacturing process, for example, silane, arsine, phosphine and the like. Examples thereof include volatile inorganic hydrides, volatile inorganic halides such as chlorosilane and chloroarsine, and organic metal compounds such as alkyl metals and metal alkoxides.

Further, in the semiconductor element manufacturing process, argon, helium, nitrogen, hydrogen, oxygen gas, etc. are usually used as a carrier gas, so the gas exhausted from the process also contains them. Argon, helium, and
It is preferable to introduce nitrogen, hydrogen or oxygen gas alone or in an appropriate mixture into the reduced pressure discharge vessel.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in detail by taking as an example the treatment for removing harmful substances such as arsine. FIG.
Shows an example of a reduced pressure discharge vessel used in the present invention. A cathode 20 and an anode 30 are arranged in a stainless steel vacuum vessel (reduced pressure discharge vessel) 10 having a gas introduction main pipe 11 and a gas discharge pipe 12. It was set up. The cathode 20 installed in the center of the container is formed in a hollow cylindrical shape, and cooling water for cooling the cathode is introduced and led out into the inside of the cathode 20 via water cooling pipes 21 and 22. Further, a heater 31 for heating the anode 30 to a predetermined temperature is provided on the outer periphery of the anode 30 installed around the cathode 20 with a predetermined distance.

A flow controller 1 is installed in the gas introduction main pipe 11.
The gas introduction pipes 14 and 14 are connected via 3, 3 and the gas discharge pipe 12 is connected to the abatement equipment 16 via a vacuum pump 15. A sampling pipe 17 for extracting the measurement gas is branched from the gas outlet pipe 12.

From the cathode terminal 23 to the cathode 20, from the anode terminal 32 to the anode 30,
A predetermined potential is applied to each, and the reduced pressure discharge container 1
0 is grounded via a ground terminal 18. Further, in the low-pressure discharge vessel 10, normally, plasma is likely to occur.
The pressure is maintained at about 01 to 10 Torr.

FIG. 2 shows that the cathode 20 has a negative potential (E _C ).
And the potential distribution when a ground potential (0 potential) is applied to the anode 30, respectively. In the plasma region P, the mass of electrons is much smaller than that of cations, so that the potential becomes nobler than the zero potential (E _P ), and the cathode end P _C of the plasma region P to the cathode 2
Over 0, a potential gradient E _a as shown in the figure is created. In addition, a potential gradient (E _b ) is also generated near the anode 30.

When argon gas containing arsine is introduced here, As ⁺ , AsH ⁺ , As
Cations such as H ²⁺ , H ⁺ and Ar ⁺ are generated, and the cations interact with the cathode 20 and the anode 30 made of, for example, copper as follows.

First, the various cations generated in the plasma region are accelerated by the potential gradient from the plasma region to the cathode and are injected into the cathode. A part of the cations implanted in the cathode is taken into the cathode as neutral atoms such as As, H and Ar by being combined with free electrons at the cathode, and the rest of the cations are in the ionic state. It is repelled by the cathode and scattered.

When cations are driven into the cathode, the kinetic energy of the cations is received and the Cu atoms at the cathode jump out and scatter. At this time, together with the Cu atoms, the As, H, and A that have already been taken into the cathode.
Atoms such as r also jump out from the cathode and are alloyed and fixed on the anode. That is, arsine, which is a harmful component, is finally captured as an alloy film on the surface of the anode to be removed from the gas, and the gas is removed.

On the other hand, part of the cations generated in the plasma region migrates to the anode due to the potential gradient in the vicinity of the anode, reaches the anode, is alloyed with Cu flying from the cathode, and is fixed on the anode surface.

Further, as shown in FIG. 3, by disposing the permanent magnet 41 together with the yoke 42 inside the cathode 20 so that a parallel magnetic field is generated in the space near the surface of the cathode, it is possible to project from the cathode during sputtering. The probability of collision between secondary electrons and arsine or argon can be increased, and as a result, the density of plasma near the cathode surface can be increased. As a result, the decomposition efficiency of harmful gas is improved, the sputtering efficiency of the cathode is improved, the number of atoms flying from the cathode to the anode is increased, and the decomposition and trapping ability of harmful components is increased. In addition, the permanent magnet is the shape (cylindrical shape, flat plate shape) and size of the cathode,
It is possible to arrange a device having an appropriate ability at an appropriate position according to other conditions.

In this way, As in the harmful components is positively ionized in the plasma state and repeats various interactions with the cathode and the anode, and finally passes through various paths to finally form an alloy film with Cu on the anode. Formed and captured.

Such action is the same as in the case of arsine other than the above. For example, in the case of phosphine, P is P ⁺ ,
After passing through cations such as PH ⁺ and PH ²⁺ , they are finally taken in as an alloyed film on the anode. The same applies to trimethylphosphine (P (CH ₃ ) ₃ ) which is an organometallic compound in which H of phosphine is replaced with a methyl group.

Also, trichlorosilane (SiHC
In the case of halides such as l ₃ ), Si also forms an alloyed film on the anode via cations and Cl is
It becomes a cation such as Cl ⁺ and similarly undergoes interaction with the cathode and the anode, and finally becomes, for example, copper chloride, which is incorporated as a compound film on the anode.

Thus, in the present invention, volatile inorganic hydrides such as arsine, phosphine, silane, germane, disilane, diborane and hydrogen selenide, halides such as dichlorosilane, trichlorosilane and trichlorophosphine, trimethylphosphine and trimethyl. aluminum,
Organometallic compounds such as triethylaluminum and tetraethoxysilane can be efficiently decomposed and removed.

In the above description, argon gas is assumed to coexist in addition to arsine as a harmful component, but this is because argon is easily cationized and discharge is maintained to improve discharge efficiency. Helium, nitrogen, hydrogen and oxygen gases can be used as well. As aforementioned,
In the manufacturing process of a semiconductor element, these gases are usually accompanied as a carrier gas, so that an appropriate amount may be added and mixed only when they are insufficient.

The material of the cathode is not limited to the above copper as long as it is a conductive substance, but since cations are driven in and heat is generated intensely, cooling means such as the above-mentioned cooling water is used. It is preferable to provide it, and in the case of copper, it is necessary to keep it at 400 ° C. or lower. Also,
Since the cathode material is scattered and consumed by the implantation of ions into the cathode, it may be replaced as appropriate according to the degree of the consumption.

On the other hand, although the anode made of copper has been described as an example, the anode is not limited to copper as long as it is a conductive substance. However, it is preferable to provide the anode with a heating means such as the above-mentioned heater, and the heating promotes the alloying or reaction between the harmful components and the anode, and the produced alloy or compound is firmly bonded to the anode material. Promote. Since the heating temperature of the anode varies depending on the material of the anode and the kind of harmful component, an optimum temperature range should be set appropriately based on experiments and the like. For example,
In the case of a copper anode, it is preferable to heat it to 100 to 500 ° C. in order to firmly capture harmful components as an alloy or a compound.

When the anode is a conductive metal and the potential distribution as shown in FIG. 2 is formed by applying the ground potential to the anode, the decompression discharge vessel is made of an insulating material such as glass or ceramic. It may be formed of a material. This anode may also be replaced appropriately depending on the degree of growth of the alloy film or the compound film.

Further, the voltage applied to the cathode may be DC or AC, and a general-purpose plasma discharge circuit as shown in the wiring example in FIG. 4 can be used. For example, as shown in FIG. 4A, a capacitor 25 is provided between the cathode 20 and the AC power supply 24 in order to generate a self-bias voltage at the cathode 20 when an AC is applied, and an anode 30 is provided at the anode 30. An appropriate voltage is applied from the DC power supply 33, and the reduced pressure discharge container 10 is grounded. In this case, it is preferable to incorporate a matching device (not shown) in order to maximize the power consumed by the discharge. Further, as shown in FIG. 4B, when a direct current is applied, direct current power supplies 27 and 34 may be connected to the cathode 20 and the anode 30, respectively, and the reduced pressure discharge vessel 10 may be grounded.

When the potential distribution as shown in FIG. 2 is formed by applying the ground potential to the anode, the decompression discharge vessel may be made of an insulating material such as glass or ceramic.

[0037]

Embodiments of the present invention will be described below. FIG. 1
The following experiment was conducted using the reduced pressure discharge vessel 10 having the configuration shown in FIG. The container is made of stainless steel having an inner diameter of 300 mm and a height of 600 mm. As the vacuum pump 15, a mechanical booster pump and a rotary pump are used in series, and the inside of the vacuum discharge container 10 is closed by a throttle valve.
Maintained at 5 Torr. The cathode 20 has an outer diameter of 1
A hollow shape having a length of 50 mm and a height of 400 mm was formed, and cooling water at room temperature was introduced to cool the inside. The anode 30 had a cylindrical shape with an inner diameter of 250 mm and a height of 590 mm, and was heated to a predetermined temperature by a heater 31 on the outer peripheral surface.

Example 1 A cathode and an anode made of copper were used, and the temperature of the anode was kept at 400 ° C. In the wiring shown in FIG. 4A, a high frequency of 13.56 MHz was applied to the cathode with a supply power of 1 KW, and a DC power source of 50 V was connected to the anode.

Argon carrier gas of 200 sccm (standard cu) was introduced into the container from a sample gas introduction pipe.
big centimeter per minute
After being introduced in step e) and plasma was generated by argon gas, arsine was supplied at 200 sccm for 60 minutes. When the arsine concentration was measured by sampling 6 times in total at 10-minute intervals from the measurement sampling tube, all were 1% or less. When the arsenic in the film formed on the anode was analyzed after the test, about 40% of arsenic was confirmed.

Example 2 The same operation as in Example 1 was carried out except that the sample gas from the sample gas introduction tube was replaced with nitrogen and replaced with nitrogen. As a result, the arsine concentration in the sampling gas was 1
% Or less. The arsenic content in the film formed on the anode was about 40%.

Example 3 The same operation as in Example 1 was carried out except that the cathode and the anode were made of nickel and the temperature of the anode was kept at 300 ° C. As a result, the arsine concentrations in the sampling gases were all 1% or less. The arsenic content in the film deposited on the anode was about 45%.

Example 4 The same operation as in Example 3 was carried out except that a high frequency of 500 MHz was applied. As a result, the arsine concentrations in the sampling gases were all 1% or less. The arsenic content in the film formed on the anode was about 40%.

Example 5 The same operation as in Example 1 was performed except that the supply amount of arsine was 100 sccm. As a result, the arsine concentrations in the sampling gases were all 1% or less. The arsenic content in the film formed on the anode was about 40%.

Example 6 The same operation as in Example 1 was carried out except that phosphine was used instead of arsine as a harmful component. As a result, the phosphine concentration in the sampling gas was 1% or less. The phosphorus content in the film deposited on the anode was about 35%.

Example 7 The same operation as in Example 6 was performed except that the high frequency was set to 500 KHz and the cathode and the anode were made of nickel. As a result, the phosphine concentration in the sampling gas was 1% or less. The phosphorus content in the film deposited on the anode was about 35%.

Example 8 The same operation as in Example 1 was carried out except that the cathode and the anode were made of aluminum, the anode was kept at 100 ° C., and tetrachlorosilane (HSiCl ₃ ) was supplied as a harmful component at 100 sccm. . as a result,
The concentrations of tetrachlorosilane and chlorine in the sampling gas were both 1% or less.

Example 9 The temperature of the anode was kept at 200 ° C., 200 sccm of arsine and trimethylaluminum ((C
Example 3 except that H ₃ ) ₃ Al) 1 sccm was supplied.
The same operation was performed. As a result, both the arsine concentration and the trimethylaluminum concentration in the sampling gas were 0.01% or less. The arsenic and aluminum in the film deposited on the anode were about 38% and 0.1%, respectively.

Example 10 In Example 1, with the wiring shown in FIG. 4 (b), a DC power of 500 W (about 500 V) was supplied to the cathode and a DC power supply of about 50 V was connected to the anode to apply DC. In addition, the anode was maintained at 200 ° C. As a result of introducing argon (200 sccm) and arsine (200 sccm) in the same manner as in Example 1, the concentration of arsine in the sampling gas was 1% or less, and the amount of arsenic in the film deposited on the anode was about 38. %Met.

Example 11 As in Example 1, a copper cathode and anode were used, and a permanent magnet was arranged in the cathode as shown in FIG. At this time, the maximum horizontal magnetic field of 1 cm on the cathode surface was 200 gauss. In the wiring shown in FIG. 4 (a), 13.5 W of power is supplied to the cathode.
A high frequency of 6 MHz was applied, a DC voltage of 50 V was applied to the anode, and the temperature of the anode was maintained at 400 ° C.

Argon carrier gas was introduced into the container at 200 sccm from the sample gas introduction tube, plasma was generated by the argon gas, and arsine was added at 400 sccm.
supplied in cm for 60 minutes. From measurement sampling tube 1
When the arsine concentration was measured by sampling 6 times at 0 minute intervals in total, all were 1% or less. After the test, arsenic in the film formed on the anode was analyzed and found to be about 31%. The deposition rate of the film deposited on the anode was about 3 times that of Example 1.

[0051]

As described above, according to the harmful gas removing method of the present invention, a volatile inorganic hydride or halide containing silicon, phosphorus, boron, arsenic, etc. discharged from the semiconductor element manufacturing process. , Or metal elements such as Si, P, B, As and C in harmful compounds such as organic metal compounds
Most of halogen elements such as 1 can be trapped and removed as an alloy or compound in the anode.

Therefore, most of the harmful components in the exhaust gas having a high concentration of harmful components can be removed, and after the harmful treatment by the method of the present invention, the well-known harmful treatment with a solid harmful agent or the like is performed. Further, it is possible to achieve more reliable detoxification, significantly reduce the load of the solid detoxifying agent and the like, and prolong the life thereof dramatically.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a reduced pressure discharge container for carrying out the present invention.

FIG. 2 is an explanatory diagram showing a potential distribution between a cathode and an anode.

FIG. 3 is an explanatory diagram showing an example in which a permanent magnet is arranged in the cathode.

FIG. 4 is a diagram showing an example of wiring.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Vacuum container (decompression discharge container), 11 ... Main gas introduction pipe, 12 ... Gas discharge pipe, 13 ... Flow controller, 14 ... Gas introduction pipe, 15 ... Vacuum pump, 16 ... Harmful equipment, 17 ... Sampling pipe, 18 ... Ground terminal 20 ... Cathode, 21, 22 ... Water cooling tube, 23 ... Cathode terminal 30 ... Anode, 31 ... Heater, 32 ... Anode terminal 41 ... Permanent magnet P ... Plasma region

Claims (4)

[Claims] 1. A plasma is generated between a cathode and an anode provided in a low-pressure discharge vessel, and exhaust gas containing harmful components is introduced into the plasma, and the cathode is cooled to a predetermined temperature to remove the anode. A method for removing harmful gases, which comprises heating to a predetermined temperature. 2. The harmful component is a volatile inorganic hydride,
The method for removing harmful gases according to claim 1, which is a volatile inorganic halide or an organometallic compound. 3. The harmful gas removing method according to claim 1, wherein at least one of argon, helium, nitrogen, hydrogen, and oxygen gas is introduced into the reduced pressure discharge vessel. 4. The harmful gas removing method according to claim 1, wherein the cathode is provided with a permanent magnet for increasing the plasma density in the vicinity of the surface of the cathode.